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Author: Subject: Detonator Casings
golfpro
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[*] posted on 22-9-2013 at 18:02
Detonator Casings


So I am trying to have caps that are as reliable, safe, and storage stable as possible. I have the materials to make an industry grade blast cap (maybe not quiet), but I don't want the casing to just be drinking straw, and risk friction and other issues. Has anyone found a way to make a nice uniform Al tube/case w/ thin walls for caps?

[Edited on 23-9-2013 by golfpro]
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Bot0nist
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[*] posted on 22-9-2013 at 18:22


Aluminum arrow shafts are where its at. Brittle and consistent... Cut off sharpie marker backs too, or small HDPE test tubes if plastic is desired. Drinking straws are a terrible idea, in my opinion. Much too flexible and elastic. Accident waiting to happen.

Play safe.




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[*] posted on 22-9-2013 at 21:06


being an archer myself, the thought of cutting my arrow shafts makes me cringe, anyway arrow shafts are expensive, why not use the cylinder of cheap ballpoint pens?
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[*] posted on 23-9-2013 at 04:21


Buy a small lathe. Use it to bore an aluminum (or steel) rod to the desired dimensions. Then use it for producing rocket nozzles, or as a starting point for a great new hobby that complements HEs nicely. Once you get some PTFE rod, you can make your own lab-ware without the glass-blowing.
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[*] posted on 23-9-2013 at 04:54


Brittle metal is usually desired over plastics so that the cap doesnt "balloon" out at the moment of initiation and create a seperation from the secondary. Metal arrows are not that cheap, but much much better than plastic pen cases. A single arrow would make many small caps I bet.

[Edited on 23-9-2013 by Bot0nist]




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bfesser
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[*] posted on 23-9-2013 at 05:43


Can't you purchase short lengths/diameters of suitable aluminum, brass, steel, and stainless steel tubing from hobby supply shops (or hardware stores)?

[edit] Admittedly, it can be expensive, but so is burning/exploding all of your chemicals.

[Edited on 23.9.13 by bfesser]




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[*] posted on 23-9-2013 at 10:13


well i think bfesser of what ive seen the tubes are too thick, what would be desired would be like a permanent marker casing, in which ive heard being used.. perhaps some stores or some online buy a tonne
of what ive seen theyre usually aluminium
otherwise guys
go buy yourself some aluminium foil tape, the thick kind..
you can then wrap this tightly around a straw and cut it however you want to, it should be possible to put on more layers to furthermore harden the external casing..




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golfpro
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[*] posted on 23-9-2013 at 18:25


I'll look in the hobby store tomorrow for something like that, but right now I have good sized cases, but they are plastic, I'd like to get an industry identical, but IMO, straw makes for good reliable initiation, but doesn't protect the materials inside very well.

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Mathias94
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[*] posted on 23-9-2013 at 22:48


I don't know what your primary of choice is, but remember that mercury fulminate and probably a lot of other primaries is uncompatible with aluminium.
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[*] posted on 23-9-2013 at 23:09


EDIT: Double post, a moderator may delete this :)

[Edited on 24-9-2013 by Mathias94]
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[*] posted on 23-9-2013 at 23:20


Copper for fulminate, Al for azide or I messed this one up badly?
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[*] posted on 24-9-2013 at 04:18


Quote: Originally posted by Mathias94  
I don't know what your primary of choice is, but remember that mercury fulminate and probably a lot of other primaries is uncompatible with aluminium.

HMTD, the most useful of the organic peroxides, should not be used with any metal other than aluminium . . .




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[*] posted on 24-9-2013 at 06:07


SADS works well with aluminum casing.
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[*] posted on 24-9-2013 at 07:25


I wonder how SADS reacts to static discharge in such an aluminium cap. I only work with visco fuse.

I wonder if the fuse, that contains (somehow conductive???) charcoal but is isolated on the outside, like a coaxcable, can create a breach in the faraday cage?

Also it leads directly to the primary, so any incoming current would have to pass the primary...



These things seem so simple, but are so complicated in detail, I'm a bit worried if this can ever be handled by hobby guys like us. IMHO such a cap must be safe to be handled once closed.

I would assume that an aluminium cap is mechanically save as long as you don't drop a big stone on it. The only thing that remains is static, especially with SADS...
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[*] posted on 24-9-2013 at 09:01


Befriend someone who works at a bow-shop. The typical process with a new arrow shaft is to trim them to length for the archer using them. The scrap typically goes into a drum for recycling.
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[*] posted on 24-9-2013 at 11:02


0.253" ID x 9/32" OD aluminum 3003 tubing is imo a perfect choice for caps. It is soft enough to form, but strong enough to handle around 5000psi during pressing. Lots of hobby shops and hardware stores have it in 1' lengths and mcmaster has it in 1' or 6'. It's cheap to boot.
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[*] posted on 5-1-2014 at 04:27
Blasting cap from paper


Hi guys,

i just thought about using paper tubes for blasting caps.

I have some pyro related spolette tubes, they are 7mm on the inside and little more than 9,4mm on the outside. Wall thickness is about 1,2mm.

I figured that these will give at least some protection for a primary while handling the cap, and no dangerous shrapnel. On the other hand, there is a zone of rather low density (compared to Al) paper between the caps booster and the secondary.

I'm not sure if paper is good or bad concerning ESD. But I read suggestions about how to package semiconductors, and I remember somehow that "paper is not too bad, also it always accumulates some moisture"

How do you feel about using paper, looking at perfomance and safety?
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[*] posted on 3-11-2014 at 17:43


Al tubing for model plane construction from hobby shops is perfect for dets.
I successfully used soft drink can aluminum when i have run out of tube though as it is quite thin.
Cut the top and bottom off an empty soft drink can and cut a small rectangle from whats left. Roll it tight round a small pen or dowel and tape. Once forcefully rolled a couple times you can get a very small tube from it.
Then push a small paper tissue plug through with the dowel to act as an end cap and fill with primary, place a fuse with some more tissue around it and tape the top. Insert into explosive when ready.
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[*] posted on 3-11-2014 at 18:04


Try using tent poles, bought for spares. Most are dreadfully thick, but some might work...
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[*] posted on 6-11-2014 at 19:31


I just found a pile of discarded arrows at my gun club archery range. They were bent or fletchings were damaged and then discarded. You can also find these things on ebay as auction lots of either functional arrows or whatnot. You can find them at a price of $1 per shaft. The trick is choosing an elegant method of closing the bottom. As a way of keeping this post scientific (here's looking at you Bert ;) )... +2 for brittle/high strength aluminum tubing. On the fracture toughness curve materials like this will absorb less energy during a charpy test demonstrating that less deformation energy is taken from the shock front... the material will deform elastically until the fracture point as opposed to a material that will transition past the elastic behavior into the plastic deformation zone and absorb energy inelastically. Though this shouldn't matter much if the quantity of primary is sufficient. And one last note, primaries don't really get characterized by critical diameter, but a composite cap with a boosting secondary should force you to compare this secondary critical diameter with the tube ID.
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[*] posted on 10-11-2014 at 15:25


22 Magnum bullet casings I think would be perfect. You could heat them red hot and crash them in water or oil to make the metal more brittle, just a suggestion.

TGT
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[*] posted on 10-11-2014 at 16:53


Quote: Originally posted by TGT  
22 Magnum bullet casings I think would be perfect. You could heat them red hot and crash them in water or oil to make the metal more brittle, just a suggestion.

TGT


What, brass? Copper alloys readily anneal even with rapid quenching.




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[*] posted on 10-11-2014 at 19:29


According to this copper alloy hardening article, you are more likely going to find non-quenchable brasses in brass cartridges. The typical path for hardening material like that is cold working, where grains are shaped by continual material damage without heating, which would cause grain growth and softening. The earlier article also mentions other methods, precipitation hardening being very common where bits of metals precipitate out of solid solution.
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[*] posted on 12-11-2014 at 11:14


Avoid metal casings like the plague. Not only do they produce nasty metal shrapnel, but also, can react with certain primaries.

Back in the day when I used to experiment with such things, I often used paper casings dipped in the "liquid glass" sodium silicate solution to give them more rigidity. A couple windings of paper around a dowel rod, fold in the end, dip the tube in the "liquid glass", and let harden up. You end up with a nice cap with thin walls (which should transmit shock better), decent rigidity, and no scary metal parts.

The same liquid glass stuff can be used for all kinds of things, like reinforcing casings of salutes and such for a louder pop.
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[*] posted on 13-11-2014 at 00:56


Also, you get a detonator that is more prone to transportation mishaps because of the lower structural strength...
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